Floors above and below zero

In winter you may hear the weather report say 'today it is −2 °C'. A number with a minus sign! This chapter is about numbers on the other side of zero. We meet Bela, who makes tasty ice cream. To make things even more fun for the children, she buys a tall building, fills it with attractions and calls it Bela's Building of Fun. But it is no ordinary building: some of its floors are below the ground!

A lift goes up and down. It has two buttons: '+' to go up and '-' to go down.

• Pressing '+' twice is written + + or +2, and takes you up two floors. Pressing '+' three times is +3.
• Pressing '-' four times is written - - - - or -4, and takes you down four floors.

You enter at the ground floor, the Welcome Hall.

• From there, pressing +1 takes you to the Food Court, so the Food Court is on Floor +1. The Art Centre is on Floor +2, and the Book Store on Floor +3.
• Pressing -1 takes you down to the Toy Store, so it is on Floor -1; the Video Games shop is on Floor -2.
• The ground floor itself is Floor 0: you press nothing to get there from the Welcome Hall.

A number with a '+' sign in front is called a positive number. A number with a '-' sign in front is called a negative number. Floors above the ground have positive numbers, and floors below the ground have negative numbers. Zero is neither positive nor negative, so we put no sign in front of it.